Presentation on theme: "Introduction Superheaters and Reheaters –Corrosion and Erosion Problems –Benefits of Chromium in Ni-Base Materials –Filler Metal 72: High Chromium and."— Presentation transcript:
Introduction Superheaters and Reheaters –Corrosion and Erosion Problems –Benefits of Chromium in Ni-Base Materials –Filler Metal 72: High Chromium and Weldable –Corrosion Examples –Application Successes
Corrosion Test Simulating Low-NOx Corrosion Conditions The test environment consisted of the following gas mixtures at 1000°F: –Reducing Cycle: N 2 -16%CO 2 -10%H 2 O-5%CO-2%H 2 S (flow rate 500 sccm). –Oxidizing Cycle: N %CO %H 2 O (CO and H 2 S turned off).
Corrosion Test Simulating Low-NOx Corrosion Conditions The test consisted of alternating cycles consisting of 4 days reducing and 3 days oxidizing. The test was conducted in a horizontal electrically heated muffle furnace having a 100mm diameter mullite tube with sealed end caps and a sealed pushrod mechanism for inserting and removing samples to and from the hot zone. Samples were cycled to room temperature and weighed at 500h, 1000h, 3000h and 4940h.
Inlet and Calculated Equilibrium Outlet Compositions for Laboratory Simulation of Low-NOx Boiler Environment at 1000°F
Corrosion Test Simulating Low-NOx Corrosion Conditions Wrought samples for alloy 625 were produced from cold-rolled and annealed sheet. The machined test samples measured ~3mm X 10mm X 20mm. Wrought samples of alloys 622 and filler metal 72 were produced from hot-rolled and solution annealed wire rod; machined test samples measured ~6mm diameter X 20mm. Weld overlay samples of filler metals 53MD and 72 were fabricated by first applying two layers of overlay onto carbon steel using the p- GMAW process followed by removal of the top layer and machining samples. The machined test sample size was ~3mm X 10mm X 20mm.
Mass change results after exposure at 1000°F (538°C) Under the Described Simulated Low-NOx Test Conditions
Reducing to Neutral Atmosphere Low Grade Coals Sulfates H 2 S Cross Section of Superheater tube.250 inches per year wastage. (Save 25) Actual Tube Cut out - Facing Gas Flow
Cross Section of Superheater Tubes from DOE – McDonald Study
Numbering of Specimens Within Test Loop Exposed in a Subcritical Coal Fired Boiler Firing 3-3.5% Sulfur Ohio Coal
Identification key for INCONEL weld overlays and alloys
Wastage as a Function of Time for Superheater tube Materials
Metal Loss As a Function of Position in Test Loop Exposed for 21,200 Hours in Coal Fired Boiler Firing 3-3.5% Sulfur Ohio Coal - Results Reported by McDonald
Wastage rate of samples exposed to °C for 21,200 Hours
Dependence of Corrosion Behavior in Synthetic Coal Ash/flue Gas Corrosion Upon Temperature - Austenitics Dependence of Corrosion Behavior in Synthetic Coal Ash/flue Gas Corrosion Upon Temperature - Austenitics Gas composition = 1%SO 2 -5% O 2 -15%CO 2 -Bal. N 2 Synthetic ash = 34%Na 2 SO 4 41%K 2 SO 4 -25%Fe 2 O 3 Reference: M. Tamura, N. Yamanouchi, M Tanimura, S. Murase, "Promising Alloys for the Heat Exchangers of Advanced Coal Fired Boilers," Proceedings : Exposition and Symposium on Industrial Heat Exchanger Technology (Materials Park, Ohio: ASM International 1985), p. 273.
Dependence of Corrosion Behavior in Synthetic Coal Ash/flue Gas Corrosion Upon Temperature - Ferritics Reference: H. Teranishi, et al, presented at the International Conference on High Temperature Alloys, Preprint Paper No. 21, Petten, The Netherlands, Oct , 1985.
Chromium content vs. wastage rate
Cross Section Loss (Depth of Attack) for High Temperature Alloys Exposed at 700°C in Laboratory Flue Gases (1% SO 2 ) Blough and Stanko: N 2 -14%CO 2 -10%H 2 O-3.6%O 2 -1%SO 2, 10% alkali sulfates Castello, et al: N 2 -15%CO %O 2 -1%SO 2, 10% alkali sulfates Baker and Smith: N 2 -15%CO 2 -4%O 2 -1%SO 2, 5% alkali sulfates Baker and Smith
Cross Section Loss (Depth of Attack) for High Temperature Alloys Exposed at 700°C in Laboratory Flue Gases (0.25% SO 2 ) Blough and Stanko: N %CO 2 -10%H 2 O- 3.6%O %SO 2,, 10% alkali sulfates Castello, et al.: N %CO %O %SO 2, 10% alkali sulfates Baker and Smith: N %CO %O %SO 2, 10% alkali sulfates Baker and Smith
Chromium + Nickel Content Versus Metal Loss
Sulfidation-Oxidation at 816°C
FILLER METAL 72 Minimum Tensile Strength: 106,000 psi Yield Strength (0.2% offset): 73,000 psi Elongation 30% AWS A5.14, ERNiCr-4 ASME IX, F-No. 43 ASME II, SFA-5.14, ERNiCr-4 ISO S.Ni6072 Europe NiCr44Ti UNS N06072 Available for GMAW or GTAW welding.
FILLER METAL 72 Super heater tube removed after in service testing. Reheater tuber overlaid with Filler Metal 72 after 2+ years of service at 1000 – 1100 o F after simulated repair weld and LP inspection
FILLER METAL 72 Hardness Profile after 2+ Years at 1000°F-1100°F
Corrosion – 209 mpy- ( Save 25)
Protection - 671
Protection from Corrosion
Protection – Filler Metal year installed
Protection – Filler Metal 72 Wastage – less than 10 mpy
Filler Metal 72 Surface Description
Sample Reheater Tube Removed from Low Nox Boiler Actual Service – 6 years
Field Success Philadelphia Electric Company Clad Reheater Tubes –9 years of service –1100 o F (595 o C) –Ave. 2.44% sulfur content –Ave. 10.8% ash content –671 unaffected by corrosion
Field Success The Outlet Leg of a Secondary Superheater. –5 ½ years of service –1000ºF (538°C) Steam –Cyclone coal fired 4.5-5% sulfur, 20% ash –No visible evidence of corrosion
Field Success The UK Central Electricity Generating Board –1974 – 1980 trouble free service –Testing led to full replacement of reheater tube –Stainless tubes had corroded at 3.5 mm/year
Field Success Large Mid-West Power Provider –Met 20 year design life –Installed Muskingum River OH and Kammer, W.V.
Field Success Fuel-Ash Corrosion-Resistance in Power Plant Steam Superheaters. –Operating temperature 1055ºF –32 months and 66 months –High sulfur pulverized coal –671 Cladding remained uniform and showed minimal corrosion
Overlaid SA213- T2 Superheater tubes installed in Rockport Unit I, Spring of Filler Metal 72 Overlay on Superheater Tubes
Overlaid SA213- T2 Superheater tubes installed in Rockport Unit I, Spring of 1999.
Filler Metal 72 Overlay on Superheater Tubes Overlaid SA213- T2 Superheater tubes installed in Rockport Unit I, Spring of 1999.
Filler Metal 72 Overlay on Superheater Tubes Overlaid SA213-T2 Superheater tubes installed in AEP R ockport Unit I, Spring of 1999.
Unifuse 360 overlay job using Spiral GMAW Followed by a GTAW pass welding process to deposit a corrosion resistant weld overlay using Alloy 72 filler metal Tubes were manufactured for use as Reheater Tubing in a coal-fired supercritical boiler - Base material was SA 213 Tp 304H 2.5 OD x mwt. - Overlay thickness average is Typical Chemical Analysis: Ni52.5% Cr41.0% Fe 6.0% Ti 0.5%
TESTING and RESULTS - Longitudinal and transverse cross-sections were cut from 5% of production (approximately 110 tubes) - Liquid Penetrant, X-Ray Flouresence and thickness measurements were made on the 5% samples and randomly on the balance of the production - None of the tests conducted revealed the presence of cracking or any major welding discontinuities. Additional to our test plan the customer performed extensive macrographic work on each of the sectioned samples (110 samples) with no evidence of defects when examined at 5X magnification.
Summary Superheaters and Reheaters - Aggressive Corrosion/Erosion Conditions. - High Chromium Content Required to Resist Molten Sulfate Corrosion. - Enhancement in Strength and Hardness Resulting from Exposure may Serve to Enhance Erosion Resistance. - Filler Metal 72 Weld Overlay Proven in the Laboratory and in the Field to Possess Superior Corrosion Resistance. - Long-Term Experience with 671 Clad Tubes Reinforces Confidence in Filler Metal 72.